net: Add skb_queue_next().

A lot of code wants to iterate over an SKB queue at the top level using
it's own control structure and iterator scheme.

Provide skb_queue_next(), which is only valid to invoke if
skb_queue_is_last() returns false.
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -485,6 +485,24 @@ static inline bool skb_queue_is_last(const struct sk_buff_head *list,
 	return (skb->next == (struct sk_buff *) list);
 }
 
+/**
+ *	skb_queue_next - return the next packet in the queue
+ *	@list: queue head
+ *	@skb: current buffer
+ *
+ *	Return the next packet in @list after @skb.  It is only valid to
+ *	call this if skb_queue_is_last() evaluates to false.
+ */
+static inline struct sk_buff *skb_queue_next(const struct sk_buff_head *list,
+					     const struct sk_buff *skb)
+{
+	/* This BUG_ON may seem severe, but if we just return then we
+	 * are going to dereference garbage.
+	 */
+	BUG_ON(skb_queue_is_last(list, skb));
+	return skb->next;
+}
+
 /**
  *	skb_get - reference buffer
  *	@skb: buffer to reference